Arduino Kit Relay and External Power Source

Hey there Project Guidance forum! I had a question about the relay that came with my Arduino Uno kit, and how it could pertain to my project. I have two power sources, the usb one used to power the Arduino, and another one used to power a light source for my project. my issues is, I need the Arduino on before I can power the project, otherwise the light would be promptly fried (as far I have come to know). the light source utilizes it's own ground, along with a ground on the Arduino board. so, the questions:

1)does the Arduino have to be powered up for the ground to work, and

2)does the relay that comes with the Arduino work for other pieces of hardware?

The relay that came with it is a 5 prong, rectangular box with not much information on it except a bunch of symbols and "5VDC" on the side.

1)does the Arduino have to be powered up for the ground to work,

If the power sources (USB/Arduino and light power) have their grounds connected together, then when the Arduino is powered down, consider all I/O pins pulled to ground (logic 0).

2)does the relay that comes with the Arduino work for other pieces of hardware?

I don't see why not. What I really don't see is the complete part# for it, but the 5VDC marking would be the required coil voltage to energize the relay.

Awesome on number one, so that kind of takes away the biggest worry (plugging the light in before the Arduino would fry the light, 12 bucks a pop).

for number two, the biggest issue I have with the relay is it lacks the (-) (+) that I've seen on the other relays on google. I was wondering if that would be an issue? I looked the kit back up online and it does confirm that it is a relay, but i'm confused to how I would set it up, especially since the website and the manual I got with it seem to lack a "relay set up" section. and any google searches takes me to a relay example using a lot more than just one relay and a simple power source.

Be careful that there are no voltages connected Arduino pins when the Arduino is powered down.

Do you have the complete part# of the relay? Is it a single relay or is it mounted on a board with connection terminals ... like this?

A link to your kit would be helpful.

the above website should take you to the page. on the page, it lacks the model number of the relay, it just says "5VDC Relay". It's shaped like a black box, and it has a few different pieces of information on it.

1st printed piece of info: JZC-11F

2nd piece of info: 005-1Z

I hope that helps.

it is not mounted on a board with connection terminals.

Here's the datasheet. It'll take 91mA to operate the 5V coil.

A circuit like the circuit below would work. The NPN transistor could be 2N2222A or similar, the diode could be 1N4148 or 1N4001 to 1N4007 or similar. I would use 1K for the base resistor (not the 10K shown). You might need a separate 5V supply to power the coil. If you're using power through the UNO's USB connector, it should be OK as long as your USB port isn't limited to 100mA.

caution do NOT try to power the relay coil from an Arduino pin, it must be connected directly to a power supply.

comm = common to both N/C and N/O
N/O = normally open, that means with no power the circuit is open
N/C = normally closed , circuit closed with no power on coil

the coil is not directional, you can connect your power either pin and ground the other pin.

this relay would be powered using an external power source, that will be used to power an external light source. it really would have almost nothing to do with the Arduino, except the microcontroller will be used to more or less to control it.